I can see lots of uses of having a login name. To name a few:
It makes socializing with other monks much easier
It allows you to tailor your answers to other monk's background, where applicable
It allows usage of the CB
It allows participation in the voting/XP system
It allows you to put a face to your statements
It allows participation in certain groups (like Janitors, pmdev etc.)
It allows customization of settings, layout, nodelets etc.
It enables taking up responsibility via the consideration system
It makes it possible to follow threads of opinions through threads of nodes. It's not so easy to discuss with three different anonymous monks with different opinions in the same thread